The present invention relates to iron-based alloys with a low coefficient of expansion and weldable and to the uses of these alloys in welded structural elements operating under cryogenic conditions, in particular for storage and transportation tanks and for pipes for conveying liquified gas.
The weldability of iron-nickel alloys having 35 to 50% of nickel, among which is the alloy known under the trade-mark "INVAR", is limited by two distinct phenomena: the tendency to a "solidification crack" and the "ductility gap". The phenomenon called "solidification crack" is due to the fact that interdendritic films are still liquid and hence unable to withstand a tensile force at a temperature where the dendrites already formed constitute a continuous solid edifice capable of transmitting the forces due to thermal contraction. The ductility gap corresponds to a ductility minimum in the temperature interval ranging from 700.degree. to 1,000.degree. C.